The invention relates to a molded case low voltage circuit breaker comprising a rotary contact bridge, a pair of stationary contacts cooperating with the contact bridge, current input conductors to the stationary contacts arranged to generate electrodynamic forces repelling the contact bridge to a repelled open position when a short-circuit occurs, a rotary bar having a transverse orifice housing with clearance the contact bridge which protrudes out from both sides of the bar, at least one pair of tension springs fitted between the bar and the contact bridge to provide a contact pressure of the contact bridge on the stationary contacts in closed position of the circuit breaker, while allowing rotation of the contact bridge to the repelled open position due to the electrodynamic forces.
In a limiting circuit breaker of the kind mentioned, the contact bridge opens quickly due to the action of the electrodynamic repulsion forces when a short-circuit occurs. High-speed breaking ensures current limiting, and as soon as the current is cleared, the contact bridge tends to return to the closed position. The return of the contact bridge to the closed position by the springs acting on this contact bridge is accentuated by bouncing of the contact bridge on the end of repulsion travel stop. These combined effects can cause reclosing of the contacts before confirmation of opening by the tripping mechanism, or before operation of the load-side circuit breaker in a selective device. A state-of-the-art circuit breaker comprises a latch holding the repelled contact in the open position to prevent any nuisance reclosing of the contacts. This device requires additional parts for latching and then for contact release.
The object of the present invention is to achieve a simple device for slowing down and possibly latching the movable contact bridge which does not require any additional parts.